1. Field of the Invention
This invention relates to the art of investment casting of metal or plastic objects by the lost wax process such as generally used in dentistry, jewelry, manufacture, and other fields; and more particularly the invention concerns an improved, elongated, tapered, sprue tube structure for spanning a long or wide casting investment, to make possible casting entire intricate dental bridge, jewelry article, artifact, work of art, or other object in one piece.
2. Description of the Prior Art
The conventional lost wax casting process generally used in industry and the arts involves fabricating a wax model or pattern of the article to be cast. Then one or more short sprue tubes are attached to the pattern; and both pattern and sprue tubes are embedded in a plaster investment. The entire assembly is then placed in an oven and heated to approximately 1800.degree. F. for a period of time until the pattern is burned out of the investment cast. The pattern cavity is then filled with a fluid casting material such as molten metal or thermosetting plastic via the sprue passages while the plaster investment is whirled in the centrifuge. After the pattern cavity is filled the assembly is cooled down and the plaster investment is broken away to release the cast article.
Heretofore when a rather large intricate object such as a dental bridge had to be cast in metal or plastic, it was generally cast in several sections which were then soldered or fused together to make the complete object. This involved a great deal of hand work which had to be done by skilled artisans. The entire process was long, laborious, and expensive. Pieces were often made oversize and were then ground down to desired dimensions. It was not possible to cast thin walled sections directly. They had to be made thicker than required and then they had to be machined down to required thinness. Often pieces were broken or damaged in the lengthy hand work process. Often cast pieces had to be discarded because they were found to have porous walls.